The following contains spoilers for Star Wars #26, on sale now from Marvel Comics.
The original Star Wars trilogy did a great job of illustrating that the galaxy was at war. From massive ships and armored walkers, to endless legions of Stormtroopers, the Empire's military machine was determined to squash the helpless Rebel Alliance. In service of this goal Emperor Palpatine unleashed the Death Star, sending an unmistakable message to the galaxy - resist and be destroyed.
In the first film, Star Wars: A New Hope, the Rebels exploited a fatal flaw in the Death Star's design to destroy the moon-sized battle station. Years later, the film Rogue One went back and explained how the Rebels stole the Death Star plans. This is now being revisited in Marvel's Star Wars #27 (by Charles Soule, Andrés Genolet, Rachelle Rosenberg and VC's Clayton Cowles), which changes canon to re-explain how the Rebel Alliance obtained the plans for the second Death Star.
The main Star Wars series has added much to the overall lore of the franchise recently. It has crossed over with both War of the Bounty Hunters and the "Crimson Reign" storyline and has detailed the rivalry between Princess Leia and the Empire's female Darth Vader, Commander Ellian Zahra. Most recently, it focused on the Rebel Alliance and their efforts to win over hearts of the residents of the galaxy.
Issue #26 introduces Lt. Jon Melton and his wife Bevelyn who were Rebel spies who secretly worrked on the construction of the second Death Star. For years, Jon and Bev were locked in by the Imperial security measures, but in this issue, they attempted to escape in an Imperial shuttle, with plans to provide the Rebellion with intormation about the new Death Star.
This is very different from the story previously established in Star Wars Legends. In the Expanded Universe, Palpatine actually allowed the Rebels to acquire the plans for the second Death Star. Marvel comics that followed the Return of the Jedi film explained how the Black Sun underlord Prince Xizor leaked information about the project to a Bothan Spynet, which then helped the Rebels track down the plans. That version was important because it proved how much that happened in the film was all part of Palpatine's plans.
Everything was a trap from the very beginning. Palpatine specifically let the Rebels know about the "unfinished" Death Star II to draw them out of hiding. As the Star Wars comic changes that story, it both takes away from Palpatine's reputation as a master manipulator and fails to explain why the Rebels thought the second Death Star wasn't operational in the film.